Causes

FXS is caused by problems with the FMR1 gene. These problems prevent fragile X mental retardation protein (FMRP) from developing. The protein helps to make connections in the brain. Without the protein, certain connections in the brain cannot be made. This causes developmental problems and prevents children from fully developing some higher cognitive functions.

Risk Factors

The main risk factor for FXS is having a parent with an FMR1 mutation. Most people who inherit a minor mutation, which is sometimes called a premutation, do not develop the symptoms and signs of FXS. A few premutated children may show signs that resemble autism. Others, primarily males, may develop a set of neurological symptoms called fragile X tremor ataxia syndrome in later adult life.

Children of mothers with FMR1 premutations are at risk of inheriting a fully mutated FMR1 gene severe enough to cause symptomatic FXS. If a woman does not have symptoms and is a carrier of an FMR1 mutation or premutation, each child of hers has a 50% chance of inheriting that gene. Of the children that inherit that gene, boys are much more likely to develop symptoms than girls. The severity of the disorder may vary between different individuals.

In general, each generation tends to have worse mutations and a higher risk of FXS than the previous one.

Symptoms

The number and severity of symptoms varies widely. Symptoms tend to be less frequent and milder in females. Symptoms can include:

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.